Metallurgical process for cold-finishing steel



" METALLURGICAL PROCESS FOR C'OLD- I p FINISHING STEEL:

Elliot S.'Nachtman, Park Forest, 11]., assignor to La Salle Steel Co., Hammond, Ind., a corporation of Delaware No Drawing. Application October 22, 1956 Serial No. 617,266 a i 9 Claims; (Cl. '14s-'-12 V This invention, relates to a metallurgicalprocess for use in the cold-finishingof steel bars, rods, tubing-,lwires;

physical properties of the steel, and it relates more particularly to a new and improved process which is apiiplicable to the cold finishing of steel to broaden mechanaical and physical properties which can be developed in the steel in various and broadened able in steels fabricated by other means heretofore employed.

In a numberof my copending applications filed concurrently herewith, description is made of further modifications and improvements in the [elevated-temperaturereduction concept wherein; in onemethod, the steel is subjected to a cold reduction step in advance of the :and other steel elements to improve mechanical and elevated-temperature reduction; in-another method, the steel .is normalized prior to advancement, through a 'die to eifect reduction in-cross-sectional area' whilethe steel is at an elevated, temperature within the range, described;

t and, in a thirdmodification, the steelis subjected to a heat-treating step to anneal the-steel prior to advancemerit of the steel through :a die ,to effect reduction in cross-sectional area while the steel is at a temperature and range of 200 F. to the lowe r criticaltemperature for the steel composition. In each of these processes described, utilization continues to be. made of thechar- 1 the steel, and to improve certain mechanical and physical ,plications of 'Nachtmanand Moore, Serial No. 518,411,

Serial No. 518,412, Serial No. 518,413, and Serial No. 518,414, filed June 27, '1955, now Patents No. 2,767,837, No. 2,767,835, No. 2,767,836'and No. 2,767,838, respective'ly.

It is an object of this invention to produce and to provide a method for producing steel'products having improved-mechanical and physical properties,

Another object of this invention is to provide aimethd which has application to the field of cold-finishing steels wherein the properties and characteristics of the steel are materially changed-to increase'the uniformity of properties and characteristics of steels of the same chemistry fromaheat to heat,- toexpand the range'of physical and mechanical properties capable of being developed in'the'steel,-to-impr0ve the. values of physical and mechanical properties of the steelyand to produce steelproductshaving new and improved characteristics and physical and mechanical properties of higher values. In the aforementioned copending applications, the inventive concepts reside in the improvement in physical and mechanical properties of steel by the processing of the steel in an elevated-temperature-reduction step wherein the steel isadvanced through a die to; take a reduction in cross-sectional'area while the steel is at a temperaturewithin the range of 200 F. tothe lower critical I temperature (l100fi-l200 F.) for the steel composition. Depending upon the 1 temperature of the steel ,4 advanced through the' die, vari ous physical and mechanical properties of the steel can be markedlyimproved byycomparison with the same steels which have been given the same reduction by advancement of the steel through the same die, but while the steel is at about room temperature. Thus, by'controlling the temperature of the steel advancedthrough the die, by controlling the chemistry of the steel, and by controlling the amount of reduction that acteristics bf the steel relating to strain-hardening and to hardening by some mode of precipitation, when worked at elevated temperature, similar to age-hardening, to produce steels having improved physical and mechanical properties The heat treatments or the coldreduction step taken-in advance of the elevated temperaturerreducw tionstep provides for no phase change of the steelbut changes are made invalues and in the range of values capable of being developed by the combination of. the described steps. i

The concepts of this-invention reside in the method of processing steel in an operation applicable to the coldfinishing of steel to cause newand improved physical and mechanical properties -to be developed in the steel by the combination of the phenomena madeavailable by taking a reduction at elevatedtemperature, as described in the aforementioned: .copending applications, but in which the steel has been treated to effect a, phase change in the steel prior tothe elevated temperature-reduction step. In accordancetwiththe praeticeyof, this invention, the steel is processed by; a combination of steps which includes heatingthe steel, to. austenitizing temperature and rapidly cooling the steel from iaustenitizing temperature to about ambient temperature to producea phase change in the; steel, tempering the steel by heat treatment to a desired temperature below the lower criticaltemperature of the ,steel composition', and then subsequently :working the steel in an elevated temperature reduction step, as, for example, by advancing the steel through a die to: efiect reduction.- in cross-sectional area while'the steelis at' a temperature within the range of 200 F. to the lower critical temperature for the steel composition, such, for example, as at a temperature within the range of 200 F. to HOW-1200 'F., The combination of steps described, which combines the phenomena of strain-hardening and age-hardening with a-phase change in the steel, produces a steel having considerably diiferent combinations of physical and mechanical properties and characteristics. The physical and mechanical properties developedin the steel dilIer in many'respects fromthe properties made available'in steels, by a cold reduction or by reduction at-elevated temperature without a phase change having previouslybeen effected 'in the steel. 1 I The process of austenitizi'ng, rapidly cooling the 'steel from austenitizing' temperature to "about room temperature, as by quenching the-steel'in oil or '"water, tempering the quenched steel, and subsequently reducin'g' "the quenched and tempered steela't "an elevated temperature results in a-simple and efficient method, capable of u'se Patented Feb. 9, 1960 in the manner described reside in the higher elasticity and impact-strength properties produced in the steel at equivalent strength levels bycompar-ison with steels processed by conventional methods or by methods. of the type described in theaforementioned 'copendiiig applications.

Included among the physical and mechanical proper ties influenced by processing'fsteelsjin "the manner described are the strength properties of thefsteel including tensile strength, impact strength,flexure strength andthe like, and other properties such as elasticity," elongation, hardness, surface roughness, machinability, proportional limits and the like. As described in'the'aforementioned copending applications, the properties of machinability, tensile strength, flexure 'strength yiel'd strength, proportional limits, impact strength, and"hardnessfare usually beneficially affected when thesteel is advanced through a' die to take a reduction incross section whilethe', steel is at an elevated temperaturein 'therangeof ZOQ F. to the lower critical temperature of thefsteehco mposition and preferably while the steel is at a temperature within the range of 450to 850 F. v

These same phenomena of improvements inphysical and mechanical propertiesof' steel by reduction at ele-' vated temperature are capable of full development in steels in which the described phase change'has' been effected by austenitizing, quenching'to about room temperature, and tempering, except that a broader'range of properties are capable of being developed with greater uniformity of properties from heat" to heat; Material and significant improvements are available in the-elasticityand impact-strengths ofthe steels at comparable strength levels, and the elevated-temperature-reduction step, capable of being taken while the steel is at a temperature of 200 to the lower critical temperature for the steel, is broadened in a preferred range'to include temperatures within the range of 200 to 900 "F.

The characteristics described are capable ofdevelo pment with hot-rolled-steels of the type which' are coldfinished by the processes of drawing or extrusion, for example. Steels' which may be used in the practice of this invention are of the type which strain-harden or harden by some mode of precipitation when worked at anelevated temperature. Representative are the plain carbon, low carbon, or high carbon and low-alloy'steels of the easy-to-draw type which, in the hot-rolledstate, include the non-austenitic steels having a pearlitic structure in a matrix of free ferrite. These are tobe distinguished from the hard-to-draw, high-speed, or carbon-toolsteels, and the high-alloy steels and stainless steels. In the process of austenitizing and quenching, the structureof-the steel is believed to be converted to a "steel which contains either bainite or martensite, alone or in combination. The quenched steel is hard to draw at room temperature, but can be drawn orotherwise reduced in cross-section when advanced through the die when the steel-is at a temperature within the range described forthe elevatedtemperature-reduction step of from 200 -F.*-to the lower critical temperature of 1100 "-1200" F. for'the steel composition, and preferably at-a temperature within the range of 200-900 F. v

In the process described, temperature and temper have an influence on. the characteristics that are developed in the steel and by properselection of the temperature at which the steel is tempered, the temperature of the steel advanced. through the die in the. elevatedrtemperature-reduction step, the amount of reduction that is taken and the chemistry of the steel, it is possible to produce steel products. of widely varying physical and, mechanical properties, and stress characteristics. to produce steel products havingnew. and improved combinations of pro-p? erties. Treatment, of the steel: after theelevated-ternpera ture-reduction step, as by slow cooling in air or by rapidly cooling, as by quenching in oil or water, bears very little material effect upon the properties developed in the steel except that rapid cooling tends to produce steels having lower levels of stress, and tends to produce steels having compressive stresses in the surface portions to provide steel products characterized by less warpage. These characteristics will become evident from the data which will hereinafter be set forth, representing the practice of this invention.

As used herein, the term elevated-temperature-reduction is meant to include the process of cold-finishing steel wherein the steel is advanced to a draw die to effect reduction in cross-sectional area while the steel is at an elevated temperature Within the range Of 200 F. to the lower critical temperature, and preferably at a temperature of 200-900 F. Included also, is the process of extruding by advancement of the steel through an extruding die or by advancement of the steel through a roller die for reduction in cross-sectional area while the steel is at the desired elevated temperature. While not equivalent from the standpoint of the process, many of the characteristics described are also. capable of development-in other processes forworking'ste'el toetfect reduction in cross-sectional area, such as by the process of rolling steels to effect reduction in cross-sectional. areawhile the steel is' at an elevated temperature within the range described. j

The phrase austenitizing andquenching is meant to embody the usual meaning of-theterm as employed in the steel trade. It includes the step of" heating the 'steelto austenitizing temperature for the steel composition, usually within the range of 1500-1600 F., followed by rapidly cooling the steel to. room temperature, ,as by means of an oil quench or water quench, to freeze the phase change in the steel whereby a steel'believed to contain bainite or martensite,.or combinations thereof,

' is produced. The .austenitized steelis :thentempered by heating the steel to a temperature below the lower critical temperature, and preferably at a temperaturewithin the range of'2001200 F., and preferably, the tempering operation is carried out by heating the .austenitized and quenched steel to'a temperature withinthe range of 400- 900 -F. The tempered steel .may be .cooled down to roomtemperature and subsequently re-heated to the desired temperature for the -elevated temperature-reduction step, or it may beadjusted directly from the tempering temperature to the temperature for elevated-temperaturereductionj a The following will illustrate'the practice of this invention,-including the affect of tempering the steel at various temperatures within the range of 200 to -1100- F., and the affectof temperature on theproperties developed in the steel when the-austenitized,=quenched, and tempered steels are advanced through the die to etfectreductio'n in cross-sectional-area whilethe steel-is at. an elevated temperature within the range described.- The concepts of this invention will hereinafter be illustrated -by-' reference to the processing of foursteels which are taken as representative-of the classes ofsteels which may be employed. Theserepresentative steels will hereinafter bereferred to as C-1018,-C 1144, (1-1080, and 4140. The following isa ladle analysis ofthese steels in which the major ingredients, other than iron, are set forthf t Y Chem y;

Grade I aaawe,

Ihe procedures for processing the steels and the conditions for testing the steels in the development of the data set forth in the following tables will. hereinafter briefly be described, along with some of the terms which are employed, as used in the specification andclaims.

PROCEDURE] I j 1 The hot-rolled steel bars, as received, arede-scaled by pickling in sulphuric acid and limed to prevent rusting.

Lime has the advantage of preventing formation of'a' tight scale in a normal furnace atmosphere at elevated temperature.

All of the hot-rolled, pickled and limed bar stock be processed in accordance with the teaching of thisinvention, was heated to the austenitizing temperature by means of a Hevi Duty electric furnace. It will be understood that other means for heating the steels to austenitizing temperature may be employed in the practice of this invention. For austenitizing, the steels were heated to the following temperature:

For quenching the steels heated to austenitizing temperature, the steels were immersed in an oil bath. It. will be understood that other means for rapidly cooling the" austenitized steel to ambient temperature may be'emeployed, and that such other means are well known to the trade.

atures desired for taking the elevated temperature re- I duction step. The steel bars were lubricated in advance of drawing with a suitable drawing compound. In the drawing step, the steels were advanced through a die having the characteristics of the die contour described in the cdpending application of Kyle, Nachtman, Landis and Kelly, Serial No. 484,726, filed January 28, 1955.

DEFINITIONS Percent reduction is meant to relate to the true reduction, as represented by the formula X 100 percent reduction [041018 Steel: Austenltlzed by he For tempering, the austenitized and quenched steels pieces are slotted through a diameter for a distance five times the diameter of the piece.

C-1018 1600 .C-1144 7 1500 C-1080 1500... 4140 1550 wherein D is the original hot-rolled diameter of the steel and D is the final diameter of the steel. The original diameters of the steels are as follows: l.

%"'round C-1144 7 round I C-1080 'round 4140 round :Proportional limits is intended to correspond to the point in the stress-strain curve where'thegreatest stress that the material is capable of sustaining without deviation from the law of proportionality ofstresst'o strain occurs (Hookes law).

Warpa'g'e factor is directly related to 'rsidualstre'ss. The warpage value is an indication of the concentration and character of the longitudinal stresses present in steel. The residual stress is obtained by means of a warpage test wherein the length of the test piece is determined as being five times the diameter plus two inches. The test The length of the slot is recorded and the maximum diameter perpendicular to'the slot is also recorded. The differences between the diameter before slotting and after slotting represents the flare caused by the presence of residual stresses. The flare is considered positive, indicative of a preponderance of tensile stresses in the steel, if thebar expands upon slotting. The flare is considered negative, indicative of preponderance of compressive stresses in the steel, 'if the ends move toward the cut made through the diam- 1 eter. The warpage values determined for evaluation are calculated on the following equation:

Warpage faotor= (L8): X

where D =the original diameter of the bar before cutting the slot D =the diameter difierential before and after cutting the slot (flare) L =length of slot Izod impact represents the impact in foot-pounds obtained by averaging the impact results from three equidistant forty-five degree notches (0.13gdeep) at 70 F. on a 0.45 diameter round x 4%" long specimen.

Hardness, represented by a diamond pyramid number (D.P.N.) was measured on a Gries reflex-testing machine employing 136 pyramid diamond at a 50 kilogram (kgl) load.

The term elevated-temperature drawing (ETD) is meant to define the taking of a reduction inthe crosssection of the steel by advancement of the steel through a die while at a temperature within the range of 200 F.

to the lower critical temperature for the steel compostion TableI ating to 1600 F. Quenehed 1n oil. Tempered at 400 F. Drawn to 17.2%

reduction. Cooled in air after drawing] V Tensile Yieldh Elongz 121. of W I Izodt Hit'gliess, D F. Stren'th Stren t tion 1. ea arpage mpac Temp of W p.s. i. p.s. i. Pei'cent Percent Factor 70 F MR v Ft.-Lbs.

Hot Roll 1 as, 375 46, 87s as. 0 67. 9 021 87. o 151 AS Quenched "a. 164, 000 109, 000 11. 5 22. 6 400 1 7. 0 i 371 H.111. uenc e 1 an I Temp red at 400 F- 109, 750 75, 000 19. 5 55. 6 240 V 43. 0 285 230 138, 000 137, 500 9. 5 42. 8 040 8. 7 343 123, 000 123,000 14. 6 62.0 2 (47. 3) 296 147, 500 147, 600 9.0 46.1 +.052 8. 7 356 I Not drawn.

Table II [O1018 Steel: Austenitized'byheating 6311600 F. Quenched in oil. Tempered at 400 F. Drawn to 17.'2%'j reduction. quenched in water after drawing] Tensile V Yield Elonga- Red. of Izod Hardness, Temp. of Draw, F. Strength, Strength, tion, 1.4, Area, Warpage Impact, DPN,

- p.s.i.- p.s.l.- Percent Percent Factor 70 F., M

Ft.l-Lbs.

Hot R011 1 68, 375; 46, 875 36. 0 67. 9 021 87. 0 151 As Quenched 1 164, 000 109, 500 11. 5 22. 0 400 17.0 371 H.R. Quenched 1 and Tempered at400 F 109, 750 75,000 19. 5 55. 6 240 43. 0 285 23 138,000 137, 500 9. 5 42. 8 040 8. 7 343 134, 250 134, 250 11. 0 48. 9 127 22. 3 280 152, 000 152,000 9. 0 38. 4 081 6. 3 356 99,000 88', 750 23. 0 67. 9 133 I (54. 3) 234 1 Not drawn. 2 Averaged value for a fibrous fracture-mot a clean break test.

Table III [C-1018 Steel: Austenitized by heating to 1600 F. Quenched to room temperature in 011. Tempered at 900 F.

W Drawn to 17.2% reduction. Cooled in air after drawing] Tensile Yield Elonga- Bed. of Izod Hardness, Temp. of Draw, F. Strength, Strength, tlon, 1.4", Area, Warpage Impact, DPN,

p.s.i. p.s.i. Percent Percent Factor 70 F.,

Ft.-Lbs.

Hot R011 1 68, 375 46, 875 36.0 67. 9 021 87. 0 151 Hot R011 As quenched 164,000 109, 500 11. 5 22.6 -.400 17.0 371 HR. Quenched 1 and Tempered at 900 F 90,750 72,000 25. 5 31. 7 -.069 2 (72. 7) 213 200 117, 750 117,500 11.5 60. 7 058 2 (46. 0) r 262 127,000 127,000 13.0 49. 7 190 25.0 291 128, 750 128, 750 13.0 55. 9 029 19.0 303 101, 750 92, 000 24.0 69. 2 0 2 (74. 7) 241 1 Not drawn. 9 Averaged values for a fibrous racturenot a clean break test.

Table IV [(3-1144 Steel: Austenitized by heating to 1500 F. Quenched to room temperatureln oil. Tempered at 1100 F. Drawn to take a 21.6% reduction. Air-cooled after drawing.)

Tensile Yield Elonga- Red. of Izod Hardness, Temp. of Draw, F. Strength, Strength, tion, 1.4, Area, Warpage Impact, DPN,

p.s.i. p.s.i. Percent Percent Factor 70 F.,

Ft.-Lbs.

Hot Roll 108, 000 70, 500 23.0 46.1 004 32. 7 220 Hot Roll 1 as Quenched 290,000 236,500 6.0 20.0 137 4. 3 492 H.R. Quenched 1 and Tempered at 1,100 F- 126,250 115,500 20.0 54. 4 046 35. 7 285 205 145, 250 125, 500 10.0 36. 2 888 35. 3 291 1 Not drawn.

Table V [04144 Steel: Austenitized by heating to 1500 F. quenched in oil. Tempered at 900 F. Drawn to take 21.6% reduction. Air-cooled after drawing] Tensile Yield Elonga- Bed. of Izod Hardness, Temp. of Draw, F. Strength, Strength, tion, 1.4", Area, Warpage Impact, DPN,

p.s.i. p.s.l. Percent Percent Factor 70 g Ft.-Lbs.

Hot Roll 1 108,000 70,500 23.0 46. 1 004 32. 7 220 Hot R011 1 as Quenched 290,000 236, 500 6. 0 20. 0 137 4. 3 492 Hot Roll Quenched and I Tempered at 900 F.... 166, 500 156,000 14. 5, 46. 5 014 25. 0 371 250 181, 750 180, 000 11. 5 42. 3 +1. 252 51. 5 350 196, 750 193, 000 ll. 0 41. 5 +1. 230 50.0 371 199, 500 198, 000 9. 0 33. 0 +1. 081 41. 0 386 213, 750 212, 500 8. 0 35. 3 +1. 017 42.0 402 195,000 193,000 12. 5 41.0 576 32.5 .402 187, 000 184, 500 11. 5 45. 3 576 35. 0 394 174, 000 168, 000 16. 0 47. 3 320 41. 0 371.v 167,000 160,000 16. 0 44. 9 199 24. 0 3649 160, 000.. 153, 750 15. 0 43.2 142 p 27.0 V 350 1 Not drawn.

Table VI [(3-1144 Steel: Austenitlzed by heating to 1500 F. Quenched in oil. Tern ered at 600 F. to take 21.6% reduction. Air-cooled afterdrawing.

Tensile Yield Elonga- Bed. of Izod Hardness, Temp. Draw, F. Strength, Strength, tion, 1.4", Area, War-page Impact, DPN,

p.s.i. p.s.i. Percent Percent Factor 70 F., MR

. FLT-Lbs.

Hot Roll 1 108, 000 70, 500 23. 0 46. 1 004 32. 7 l 220 Hot Roll 1 as Quenched 290, 000 236, 500 6.0 20. 0 137 4. 3 l 324 H.R. Quenched 1 and T Tempered at 600 FL... 245,000 216,000 0 28. 9 044 2 7 318 275 +2. 550 378 390 3 +1. 532 420 530 222,000 -0 J 0 +1.552 9.3 J 511 600 270,000 268,000 0.7 2.2 +1. 329 9.0 526 247, 000 243, 000 4. 3 14.5 +1. 075 8. 7 490 220,000 211,000 9. 7 34. 5 651 15.0 438 176,000 172, 500 11. 0 46. 1 085 25.0 370 154,500 150,500 13.0 47. 7 064 37. 6 330 135,000 128, 500 15.0 50.1 i-. 035 52.0 296 Notdrawn. I 3 [Bars split in half when out on the abrasive saw about 24 hours after drawing cycle] Table VII [13-1144 Steel: Austenitized by heating to 1500 F. Quenched in oil. Tempered at 400 F. Drawn to take 21.6% reduction. Air-cooled alter drawing] Tensile Yield Elonga- Bed. of Izod Hardness, Temp. of Draw, F. Strength, Strength, tron, 1.4, Area, Warpage Impact, DPN,

p.s.i. p.s. Percent Percent Factor F., MR l Ft.-Lbs.

Hot Roll 1 108, 000 70, 500 23.0 46. 1 004 32. 7 220 Hot Roll 1 as quenched 290, 000 236, 500 6.0 20. 0 137 4. 3 324 H.R. quenched and szo'l lempered at 400 F.-. 297,500 175, 500 7. 9 22. 2 093 4 0 330 347, 000 341, 500 4. 3 16. 0 +1. 718 610 272, 000 269, 000 6. 0 31. 7 818 7. 3 526 214, 000 212, 500 11. 0 43. 5 505 37. 0 438 207, 250 204, 000 '13. 0 42. 3 484 27. 7 429 178, 000 170, 500 14. 5 45. 3 299 25. 0 386 162, 750 .154, 500 17. 5 47. 7 31.3 343 I Not drawn. 1 [Short specimen-Bar broke upon drawing] Table 1 VIII A [(3-1080 Steel: Austenitized at 1500 F. Tempered at 1200 F. Drawn to take 15.7% reduction. Air-cooled after drawing] Tensile Yield Elonga- Bed. of Izod Hardness, Temp. of Drew, F. Strength, Strength, tion, 1.4, Area, Warpage Impact, DPN,

p.s.i. p.s.i. Percent Percent Factor F., MR

Ft.-Lbs.

Hot Roll 1 144, 500 V, 76, 000 12. 5 17. 0 025 4. 7 296 Hot Roll 1 as Quenched. 3 204, 000 061 2. 0 436 H.R. Quenched 1 and Tempered at 1,200" F. 133, 500 103,000 21.0 41. 9 002 34. 7 276 154, 250 133, 000 12. 5 43. 2 039 20. 0 324 152, 000 128, 000 13. 0 38.4 22. 0 301 152, 250 138, 750 12. 5 41.9 101 21. 7 312 158, 500 153, 000 9.0 41. 5 070 16. 0 324 169, 500 169, 500 7. 0 36. 2 031 13. 0 312 170, 250 170, 000 9. 0 40. 2 008 12. 7 318 152, 750 142, 000 14.0 34 8 070 22. 0 307 142, 000 124, 500 16. 5 40. 6 054 31. 7 296 132, 500 107, 500 20.0 38. 9 023 38. 7 v 285 1 Not drawn. e I 0 Estimated from averaged hardness values of quenched specimens-Material appears to he very brittle and dimeult to machine in the as quenched" condition.

Ta'bleIX [0-1080 Steel: Austenitlzed at 1500 1. Tempered at 700 F. Drawn to take 15.7% reduction. Air-cooled after drawlng.]

Tensile Yield Elonga- Red. of Izod Hardness, Temp. 01 Draw, F. Strength, Strength, tion, 1.4, Area, Warpage Impact, DPN,

p.s.i. p.s.i. Percent Percent Factor F. MR

Ft.-Lbs

Hot Roll 1 144, 500 76,000 12 5 17. 0 025 4. 7

Hot Roll 1 as Quenched. 2 204, 000 061 2. 0 436 BLR. quenched 1 and l l q Tempered at 700 F---. 256, 000 217, 500 10. 0 25. 1 093 5. 3 490 300 0 0 140 4. 0 502. 340.-- 0 0 318 4. 0 "448 410--- 0 0 210 4. 0' 429 580.-- 3. 6 14. 1 +.140 5. 3' 438 620 6. 4 21. 6 194 5. 6 479 1 Not drawn.

I Estimated lrom averaged hardness values of uenchedspcimens-materlal appealrs, to bewery; brittle.

and diflicult to machine in the "as quenched" con ltion.

[4140 Steel: Austenitized at 1550 F. Tempered at 1100 F. Drawn to take 19.9% reduction. Air-cooled after drawing] Tensile Yield Elonga- Red. of Izod Hardness, Temp. of Drew, F. Strength, Strength, tion,'1.4, Area, Warpage Impact, DPN,

p.s.i. p.s.i. ..Peroent Percent. Factor F., MR

Ft.-Lbs.

Hot Roll 1 140,000 105, 750 15.0 42. 8 004 9. 0 307 Hot Roll 1 as Quenched 286, 000 231, 000 12. 1 42.8 409 25. 7 448 HR. Quenched l and Tempered at 1,100 F- 159, 000 149, 750 17. 5 62.0 018 52. 0 356 250 181, 000 173, 750 13. 0 55. 6 077 1 46. 3) 350 172,000 12.5 52. 5 121 9 47.0) 356 179,500 14.5 56.3 +.083 2 542.0) 371 190,000 12.5 55.2 +.l 9 48.0) 378 189, 500 13.0 53. 2 147 2 E37. 0) 386 177, 500 17. 5 55. 9 281 2 45.0) 386 168, 000 17. 5 50. 9 077 50. 5 371 153, 750 21. 0 59. 5 121 i (63. 0) 343 1 Not drawn. 1 Averaged values for fibrous fracture-not a clean break test.

Table XI [4140 Steel: Austenitized at 1550 F. Tempered eta-6002. 1?.1 Drawn to take 19.9% reduction. Air-cooled after aWllllg- Tensile Yield Elonga- Bed. of Izod Hardness, Temp. of Drew, F. Strength, Strength, tion, 1.4, Area, Warpage Impact, DPN,

p.s.i. p.s.i. Percent Percent Factor 70 F., MR

Ft.-Lbs.

Hot Roll 140,000 105, 750 15.0 42.8 004 9.0 307 Hot Roll 1 as Quenched" 286, 000 231, 000 12. 1 42. 8 409 25. 7 448 H.R. Quenched 1 and Tempered at 600 F 262, 000 225, 000 13.0 49. 7 077 .12. 7 539 500 279, 000 0 0 396 7. 3 594 275, 000 0 0 491 10. 7 565 261, 000 247, 500 9. 3 41. 0 517 16. 7 513 206, 500 206, 500 14. 5 44. 9 287 33. 0 429 179, 750 179,500 19.0 58.1 064 2 (53.7) 386 154,000 153,000 22. 5 62.0 +.013 I (51'. 3) 330 1 Not drawn. Averaged values for fibrous fracture-not a clean break test.

It will be apparent from the foregoing that-the parabolic curve characteristic of the strength properties de. veloped by elevated temperature reduction (ETD) without austenitizing, quenching and tempering is'also capable of development in steels processes in accordance with the The range of properties of the austeniments in tensile strength, yield strength andhardness in steels processed in accordance with the teachings of this invention over correspondingly austenitizecl, quenched and tempered steels drawn to eiiect. an equivalent re duction at ambient temperature. The same improvements are generally made available whether the drawn steel is air-cooled or quenched after drawing. Ductility, as measured by percent elongation and reduction of area, is improved by elevated temperature reduction over cold drawing for the austenitized, quenched, and tempered T steels for both air-cooled and quenched steels.

Residual stress as measured by warpage stress is improved also but mostly in high-tempered quenched steels, such, for exam ple, as the C1018 steel.

Izod impact is improved in both aircooled and quenched steels which have been tempered after austenitizing. V

The data hereinafter set forth compares the properties this invention, with the properties available in the same steels during various stages of the process and with other methods for processing'the same steels to take the equivalent reduction at equivalent temperature, as in the elevated temperature reduction process of the aforementioned copending applications. In the presentation of data on steels reduced at elevated temperature, the values set forth are arbitrarily selected to represent the better of the values for the respective properties in steels processed within the described temperature range. For example, the better tensile strength and yield strength properties will be found in steels drawn at a temperature withinthe range of about 400 -900 F. while the better values of elongation and reduction in area will be found in the steels drawn at a temperature within the upper portion of the elevated temperature reduction range.

In the tables, the following abbreviations have been used:

AQT CD=austenitiZed and quenched steel which. has

been tempered at 900 F. and drawn at ambient temperature.

AQT D austenitized and quenched "steel which has been tempered at 900 F. and drawn at elevated tem-' capable of being developed in steels by the practice of' perature."

Comparison of the data will show that austenitizing.

and quenching followed by reduction at elevated temperature provides improvements in properties over the same steels which have been merely subjected to an elevated temperature reductionstep from the standpoint of tensile strength, yield strength,- and'hardness for both air cooled and quenched specimens. Ductility and impact strengths are also improved by the practice of this invention as compared to elevated temperature reduction or cold reduction without previously having effected a phase change by austenitizing and quenching. The residual stress characteristics are somewhat of the same character as are secured by elevated temperature reduction alone. I

It will be apparent'from the foregoing that the combination of steps embodied in the practice of this invention is capable of use to produce steels having new and improved combinations of properties and in which various of its properties, such as its strength properties, elasticity, hardness, and machinability are materially improved over values which are capable of being secured in equivalent steels by other conventional cold finishing systems which have heretofore been employed.

It will be understood that changes may be made in the detai-ls of handling and processing without departing from the spirit of the invention, especially as defined in the following claims.

1. The metallurgical process for treating steel of'the nonaustenitic type having a pearlitic structure in a matrix of free ferrite comprising the combination of steps of heating the steel to austenitizing temperature and quench-- operation while the steel is'at a temperature within-therange of 400 F. to the lower critical temperature for the steel composition. 7

2. The metallurgical process for treating steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite comprising the combination of steps of heating the steel to austenitizing temperature and quenching the steel to form martensite, tempering the steel, and advancing the tempered martensitic steel through an extrusion die to efiect reduction in cross-sectional area in the extrusion operation while the steel is at a temperature within the range of 400 F. to the lower critical temperature for the steel composition. I

3. The metallurgical process for treating steel which strain-hardens and which hardens by some mode of precipitation when worked at 'atemperature between 200 F. and the lower critical temperature for the steel composition comprising the combination of steps of heating the steel to austenitizing temperature and quenching the steel to form martensite, tempering the steel by heating to a temperature below the lower critical temperature-of the tempered martensitic steel composition, and advancing the steel through a die to effect reduction in cross-sectional area while the steel is at a temperature within the range of 400 F. to the lower critical temperature for the steel composition.

4. The metallurgical process for treating steel which strain-hardens and which hardens by some mode of precipitation when worked a't'a temperature between 200 F and the lower critical temperature for the steel composition comprising the combination of steps of heating .the steel to austenitizing temperature and quenching the steel to form martensite, tempering the steel by heating 1 to a temperature below the lower critical temperature of the tempered martensitic steel composition, and advancing the steel-through a draw die to effect reduction in cross-sectional area by a draw operation while the steel is at a temperature within the range of 400 F. to the lower critical temperature for the steeel composition.

5. The metallurgical process for treating steel which strain-hardens and which hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition comprising the combination of steps of heating the steel to austenitizing temperature and quenching the steel to form martensite, tempering the steel by heating to a temperature below the lower critical temperature of the tempered martensitic steel composition, and advancing the steel through an extrusion die to effect reduction in cross-sectional area while the steel is at a temperature range within 400 F. to the lower critical temperature for the steel composition.

6. The metallurgical process for treating steel which strain-hardens and which hardens by some mode of precipitation when Worked at a temperature between 200 F. and the lower critical temperature for the steel composition comprising the combination of steps of heating the steel to austenitizing temperature and quenching the steel to form martensite, tempering the steel by heating to a temperature below the lower critical temperature of the tempered martensitic steel composition, and rolling the steel to effect reduction in crosssectional area by therolling operation while the steel is at a temperature within the range of 400 F. to the lower critical temperature, for the steel composition.

7. The metallurgical process for treating steel which strain-hardens and which hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition comprising the combination of steps of heating the steel to austenitizing temperature and quenching the steel to form martensite, tempering the steel by heating to a temperature below the lower critical temperature of the steel composition, and advancing the tempered martensitic steel through a die to efiect reduction in crosssectional area'while the steel is at a temperature within the range of400 F. to the lower critical temperature for the steel composition and air-cooling the steel after advancing" through the die in the elevated-temperaturereduction step.

8. The metallurgical process for treating steel which strain-hardens and which hardens by some mode of precipitation when worked at a temperature between 200 F. and the lower critical temperature for the steel composition comprising the combination of steps of heating the steel to austenitizing temperature and quenching the steel to form martensite, tempering the steel by heating to a temperature below the lower critical temperature of the steel composition, advancing the steel through a die to efiect reduction in cross-sectional area while the steel is at a temperature within the range of 400 F. to the lower critical temperature for the steel composition and quenching the steel rapidly to cool the steel after advancement through the die at elevated temperature.

9.- A steel product having new and improved physical and mechanical properties produced by the method of claim 3.

References Cited in the file of this patent UNITED STATES PATENTS 1,018,369 Potter Feb. 20, 1912 2,435,511 Rice Feb. 3, 1948 r 2,448,753 Weesner Sept.'7, 1948 OTHER REFERENCES Alloys of Iron and Carbon, vol. 1, Epstein, pp. 177-178, 1936.

Metal Progress, May 1.945, p. 938.

Dunn: Iron & Steel Engineer, pages 51-57 and 77, July 1946.

Bullens: Steel and Its Heat Treatment, pages 311-326, 1948. 

1. THE METALLURGICAL PROCESS FOR TREATING STEEL OF THE NON-AUSTENITIC TYPE HAVING A PEARLITIC STRUCTURE IN A MATRIX OF FREE FERRITE COMPRISING THE COMBINATION OF STEPS OF HEATING THE STEEL TO COMPRISING THE COMBINATION OF STEPS OF ING THE STEEL TO FORM MARTENSITE, TEMPERING THE STEEL, AND ADVANCING THE TEMPERED MARTENSITIC STEEL THROUGH A DRAW DIE TO EFFECT REDUCTION IN CROSS-SECTIONAL AREA IN A DRAWING OPERATION WHILE THE STEEL IS AT A TEMPERATURE WITHIN THE RANGE OF 400*F. TO THE LOWER CRITICAL TEMPERATURE FOR THE STEEL COMPOSITION. 